1. Field of the Invention
This invention relates to a method for processing integrated circuit structures. More particularly, this invention relates to an improved process to smooth a non-planar surface in an integrated circuit structure.
2. Description of the Prior Art
In the construction of high density integrated circuit structures, it is necessary to form many layers over the substrate. While the initial substrate is flat and smooth, the imposition of active devices, lead lines, contact vias, etc. thereon results in a non-planar surface with steps which must be smoothed out before subsequent layers maybe accurately applied. Planarization processes to accomplish such smoothing have become very important as the need for higher density integrated circuit structures has increased the number of layers utilized.
Gwozdz U.S. Pat. No. 4,451,326, assigned to the assignee of this invention, describes and claims a method for planarization wherein a sufficient amount of photoresist is deposited over an insulating layer having steps therein to fill in the low spots. The layers are then etched using an etchant which will remove both the photoresist material and the insulating material at about the same rate. This results in the removal of insulating material from the high spots while photoresist is removed from the low areas to thus smooth out the steps upon subsequent removal of the photoresist.
Thomas et al U.S. Pat. No. 4,481,070, also assigned to the assignee of this invention, describes and claims a double planarization process wherein a first insulating layer is planarized generally in accordance with the method described and claimed in the aforementioned Gwozdz patent and then a second insulating layer is applied over the first layer and the structure is again planarized.
While the foregoing methods are satisfactory to planarize the overall topography of the layers, it has been found, in some instances, that the surface of the insulating layer, after planarization, comes out with a roughened microtexture as shown in the photomicrograph of FIG. 1 which illustrates a surface after planarization by prior art processing.
It would be desirable to provide as smooth a surface as possible after such planarization to improve the lithography of subsequent layers formed over the planarized layer. It would be equally desirable to provide smooth surfaces in other applications including other applications where a photoresist is used as a mask in an etching process. Quite surprisingly, I have discovered a technique which eliminates the problem of roughened surfaces which may occur during certain processing of an integrated circuit structure which involves the use of photoresist.